This invention concerns closed cycle cooling systems and more particularly those of miniature type. As is known, such systems include as basic parts thereof two major components, viz. the compressor unit and the expansion unit. One group of such coolers is of the so called "split type" wherein compressor and expander units are strictly separate from one another and are interconnected by a gas conduit or conduits.
In the split type cooler belonging to the Stirling thermodynamic cycle kind, there is provided a compressor including a crank shaft driven by an electromotor. A piston actuated by the said shaft creates the required pressure pulses.
In the last named type of cooler the electromotor is conventionally located within the gaseous atmosphere, i.e. the gas used in operating the compressor. Obviously specially designed motors have to be employed.
Now, as is known, one of the reasons for faulty performance of the cooler is contamination of the gas, caused to a large extent by residual gas remaining in the system after precleaning or due to evaporation of high pressure material in the interior of the cooler. So, e.g. organic varnishes used for insulating rotor and stator windings of the motor are a main source of gas contamination.
A further fact to be considered is that in the compressor unit converting electrical energy into mechanical energy unavoidably heat is created--being a waste--which must be removed from the compressor by means of natural or forced convection or solid conduction.
The motor, being located within the working gaseous atmosphere presents certain problems of maintenance, since--in order to reach it--the region where gas is contained in, has to be opened to the air.
It is now proposed--in order to do away with the inconvenience of maintenance of the motor located within a gaseous atmosphere--to use an ordinary--not specially designed--electromotor and to locate it at the exterior of a gas enclosing housing and to provide a magnetic torque-coupler for the rotational transfer of drive from the electromotor to the compressor crankshaft located within a casing in relation to which the motor is exteriorily located.
An additional advantage from a thus exteriorily placed motor can be derived by providing a fan at the end of the motor shaft which is opposite the driving end thereof (carrying the magnetic couple) and this way create an uninterrupted flow of air onto and about the housing in which the compressor unit is contained and so remove the heat by forced convection.